The present invention reveals a wearable, wireless, non-invasive device applicable to the hand or foot, a wireless system and method for reducing the risk of different critical situations of hypoxia and/or bradycardia that could happen in the sudden infant death syndrome (SIDS), Pierre Robin Sequence patients, preterm babies and adults and for the prevention of the Sleep Apnea. The device is based on the use of a sensor and a computing algorithm sufficient to reduce false alarms and save lives. The device is worn on the hand or foot of the user. Part of the device may be placed on the proximal phalange of a finger or a foot, or even in the palm. The electronics of the device may be placed inside gloves or booties of different sizes to accommodate the hands or feet of different wearers. The device measures blood oxygen saturation and heart rate through a sensor that is preferably a pulse oximeter. The device is designed to first monitor if non-zero numeric values of heart rate or blood oxygen saturation are measured. If this is not verified it will assume the device is not working correctly or is placed off its correct position. When either measured blood oxygen saturation values or heart rate are detected and falls below certain assignable and pre-adjusted thresholds, a complex algorithm is activated. This algorithm activates specific timers which are able to measure elapsed time of periods during which the device detects values below threshold for blood oxygenation values and/or heart rate. If either heart rate or blood oxygenation is found to be at a pathological level (that is below or above certain thresholds) for a period longer than a preset safety trigger delay of the timer, an electric discharge is delivered to stimulate the wearer's reaction and a local and/or remote alarm occurs. These alarms can be received in devices such as smartphones or remote computers. The future miniaturization of this device could allow making the device as small as a ring, with the electrodes disposed around the finger. Also the device can fit in a wrist band, with the electrodes disposed in some region of the wrist.